feat(claim): arbitration per mode (#5) — first claim wins except conspiracy (#23)

nestapi.go

@@ -132,6 +132,17 @@ func (s *Server) postNestMessage(w http.ResponseWriter, r *http.Request) {
 	// Mode (Epic C, same rule shape as kind): Jev first, header escape, "" when unsure.
 	mode, modeBy := s.tagMode(kind, body.Mode, body.Text)
 
+	// Claim arbitration (#5, Epic C): first claim wins unless the referent is a
+	// conspiracy, which expects multiple claims.
+	if kind == "claim" && body.RefersTo != "" {
+		if origin, found := s.msgs.ByMsgID(body.RefersTo); found && origin.Mode != "conspiracy" {
+			if owner, claimed := s.msgs.FirstClaim(origin.NestID, origin.MsgID()); claimed {
+				httpError(w, http.StatusConflict, origin.MsgID()+" is claimed by "+owner+"; review it instead of redoing it.")
+				return
+			}
+		}
+	}
+
 	msg := Message{
 		NestID:     nestID,
 		Kind:       kind,